Head positioning and monitoring are important for a variety of electromechanical systems. One such system is a disc drive, in which one or more heads are configured for selective access to a respective movable surface. Disc drives are a convenient and cost-effective way to store data. They can use rigid discs coated on one or both major surfaces with a magnetizable medium for storing digital information in concentric data tracks. The disc(s) can be arranged for rotation on a spindle motor which causes the disc(s) to spin.
Heads carrying transducer elements are supported relative to the respective disc surfaces to transfer digital information to or from selected tracks. Each head creates an air bearing surface which faces the corresponding disc surface. As the disc rotates, the disc drags air onto the head along the air bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the air bearing surface, the pressure between the disc and the air bearing surface increases, which creates a hydrodynamic lifting force. To fly, the head generates a lifting force sufficient to overcome a preload force supplied to bias the head toward the disc surface. The hydrodynamic properties of the head are affected by the speed of rotation of the disc, the design of the air bearing surface of the head, and the preload force supplied to the head gimbal assembly.
When not in operation, each head can be parked on a designated area on the disc surface. For example, discs can include both a landing zone and a data zone on a common major disc surface. Data is stored in the data zone. Landing zones are used to support the head when the disc drive is not in operation and provide a takeoff and landing surface for the head. Such landing zones contain no data because repeat contact by the head could eventually destroy any data stored.
Textured landing zones can be used to provide a roughened surface for reducing stiction between the head and the disc surface for takeoff. Texturing is formed on a disc surface by a laser technique or other technique to provide a surface for the head to take off and land. Bumps provide lower contact area between the head and disc surface to lower the stiction force holding a stationary head to the disc surface.
Other designs use a cam or ramp to unload the head (away from the disc) when not in use. Each arm that supports a head can include a load tang, for example. A seek operation is performed that moves the head toward the cam or ramp. As the head continues this (lateral) movement, the load tang comes into contact with slides up onto the cam or ramp, lifting the head away from the disc surface as it goes.
One problem with any of these designs is the risk that the head may not be where it should on an initial power-up, or following a spin-down of unknown duration. Thus it is possible that the head may be in contact with some portion of the data surface, unlatched or in some other undesirable condition before the disc drive is readied for operation. What is needed is an effective way to monitor and diagnose such situations before a catastrophic loss of data occurs.